1. Field of the Invention
The present invention relates to a transmission power control method for controlling transmission power of an enhanced dedicated physical data channel for transmitting uplink user data, a mobile station, and a radio network controller.
2. Description of the Related Art
In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional radio network controller RNC, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2(b), or, as shown in FIG. 2(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2(b) and 2(c).
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
In “Enhanced Uplink”, a MAC-layer function, which is implemented in a radio base station Node B, is configured to control a transmission rate of uplink user data transmitted by a mobile station UE, using two transmission rate control channels described below. (See, Non-Patent literature 1:3GPP TS25.309 v6.1.0)
As a first transmission rate control channel, an “Absolute Rate Grant Channel (AGCH)” is used for controlling the transmission rate of uplink user data.
The AGCH transmits, from the MAC-layer function located in each cell of the radio base station Node B, an absolute value for a maximum allowable transmission rate of uplink user data (or parameter relating to the maximum allowable transmission rate) to each mobile station UE (individual mobile stations or all mobile stations).
Here, the above-described parameter relating to the maximum allowable transmission rate is a transmission power ratio between an “Enhanced Dedicated Physical Data Channel (E-DPDCH)” and a “Dedicated Physical Control Channel (DPCCH)” (i.e., transmission power of E-DPDCH/transmission power of DPCCH) and the like.
The increase/decrease of the parameter relating to the maximum allowable transmission rate is corresponding to the increase/decrease of the maximum allowable transmission rate, and it is acquired in connection with the maximum allowable transmission rate.
As a second transmission rate control channel, a “Relative rate Grant Channel (RGCH)” is used for controlling the transmission rate of uplink user data.
The RGCH transmits, from the MAC-layer function located in each cell of the radio base station Node B, a downlink command indicating relative values such as an “Up Command”, a “Down Command”, a “Keep Command”, or the like, for a maximum allowable transmission rate of uplink user data (or parameter relating to the maximum allowable transmission rate) to each mobile station UE (individual mobile stations or all mobile stations).
Firstly, when the mobile station UE transmits uplink user data, the mobile station UE determines a maximum allowable transmission rate of uplink user data in the mobile station UE (or a transmission power ratio between the E-DPDCH and the DPCCH, or the like) using the AGCH and the RGCH.
Secondly, the mobile station UE determines a transmission data format (transmission data block size, or the like) for transmitting uplink user data, based on the buffer residence transmission data size in the mobile station UE.
Thirdly, the mobile station UE determines the transmission power ratio between the E-DPDCH for transmitting uplink user data and the DPCCH, or a transmission wave amplitude ratio between the E-DPDCH and the DPCCH, based on the determined transmission data format (hereinafter, a gain factor).
As shown in FIG. 3, the gain factor and the transmission format number is corresponding on a one-on-one basis. The radio network controller RNC is configured to notify a gain factor correspondence table to the mobile station UE, when a call connection is performed. In the gain factor correspondence table, as shown in FIG. 3, the transmission format number and the gain factor is corresponding. In order to notify the gain factor correspondence table, from the radio network controller RNC to the mobile station UE, two schemes have been proposed.
The first scheme is a “Signaled Gain Factor”. When the “Signaled Gain Factor” is applied, the radio network controller RNC notifies the gain factors to be set in all of the transmission formats.
The second scheme is a “Computed Gain Factor” (See, FIG. 4). When the “Computed Gain Factor” is applied, the radio network controller RNC notifies the gain factors to be set in one or a plurality of transmission formats. Here, the transmission formats to which the gain factor to be set is notified is called as a “Reference transmission format”.
A transmission format except for the reference transmission format is called as a “Normal transmission format”. When the normal transmission format is used, the mobile station UE is configured to calculate a gain factor of the normal transmission format, by using the gain factor of the reference transmission format and a predetermined calculating formula.
A simple formula for calculating a gain factor of the normal transmission format is to multiply the ratio between a transmission data block size of the normal transmission format and a transmission data block size of the reference transmission format by the gain factor of the reference transmission format.
As described in a Non-Patent literature 2 (3GPP TSG RAN WG1 R1-050215), in the conventional method, a gain factor of a normal transmission format is calculated using a reference transmission format having a maximum transmission data block size among reference transmission formats having a transmission data block size smaller than the transmission data block size of the normal transmission format, when acquiring the gain factor of the normal transmission format.
Therefore, as shown in FIG. 4, the transmission format having a smallest transmission data block size has to be the reference transmission format. Thus, in FIG. 4, a transmission format number for reference referring to “*” is the reference transmission format.
However, the transmission format having the smallest transmission data block size can not get an error correction encoding benefit, therefore a transmission power for the transmission format having the smallest transmission data block size have to be set higher per one bit, compared with a transmission format having other larger transmission data block size.
Therefore, in order to set appropriate transmission power, and to increase a transmission efficiency, a transmission data block size of the reference transmission format having a second smallest transmission data block size needed to be smaller.
For the above reason, there has been a problem that the reference transmission formats have to be provided closely, otherwise an excessive gain factor is used for transmitting by using a transmission format having a relatively large transmission data block size.
In other words, there is a problem that an increase of a volume of control signals, an increase of complexity of hardware, an increase of test operations, and an increase of system operations occurs, because a lot of reference transmission formats are set.